A Proposed Regional System of Categorizing Wet Bulb Globe Temperature for Athletic Outdoor Policy

Exertional heat illnesses affect thousands of athletes each year across the United States. The Wet Bulb Globe Temperature (WBGT) is a common measure of heat exposure used widely in athletics, the military, and occupational safety. Many interscholastic athletic programs rely on heat safety guidelines established by The American College of Sports Medicine (ACSM) which use the WBGT. These guidelines, however, employ fixed thresholds that neglect regional variations in acclimatization to heat. It is well known that there are geographically diverse exposure-response relationships for heat morbidity and mortality related to regional acclimatization. Here, a modeled climatology of WBGT (1991-2005), consisting of data from around the contiguous United States, is used to identify geographic patterns of various warm season (May-September) local extreme WBGT values. The data reveal large regional variability in extreme WBGTs across the country, indicating that a “one size fits all” approach to heat safety categories is insufficient. We develop three sets of heat safety categories using the 90th WBGT percentile as the critical cutoff for canceling exercise: ≥ 32.3°C as category 3, 30.1-32.2°C as category 2, and < 30°C as category 1. It is our hope that these preliminary categories will serve as a foundation for promoting future changes to preexisting heat safety protocol.